Here's a clock for geeks. It's $20 on Etsy.
Explanation of clock numerals:
2 "An infinite number of mathematicians…"
3 A Unicode character as a HTML entity
5 The Golden Mean reworked a little
7 6.99999.. Though a different number than 7, still equals 7
8 Graphical representation of Binary code
9 An example of a base-4 number